I use welding oxygen for my medical grade ozonator. If it worries you at all, they make little inline filters to filter out small particles that may reside in the tank (I think you can purchase from plasmafire.com).
I've seen those on ebay and don't know alot about them. I know they claim to be medical grade. If I were you I'd try to get them to give you some more specifics, with such information as every material used on the ozone path, and as much detail about the internals as possible. If they do give you more info, you could post the info here and someone may be able to advise you further.
I will have to say that they win the award for the coolest case out of any ozonator I've ever seen.